Foreign Secretary William Hague today ruled out fresh concessions to the Liberal Democrats if they fail to secure victory in next month's referendum on voting reform for Westminster elections.

Mr Hague brushed off an outspoken attack by Deputy Prime Minister Nick Clegg who accused David Cameron of "defending the indefensible" in his opposition to the alternative vote (AV) system.

In an interview with The Independent on Sunday, Mr Clegg denounced the No to AV campaign for its "lies, misinformation and deceit" and said he hoped it marked the final death rattle of a "nasty right wing clique".

Mr Hague acknowledged that feelings were running high ahead of the referendum vote on May 5, with Conservatives and Liberal Democrats campaigning against each other.

However, he insisted that it would not affect the work of the two parties in the coalition.

"These things do get bandied about in a referendum campaign. Feelings run high, people get excited. I think the important thing for people to know is the coalition is working well together. It continues to work well together," he told BBC1's The Andrew Marr Show.

"Yes, we all have strong feelings about it and I very much hope people will vote No, but at the end of it the coalition will be working very well together."

Lib Dem deputy leader Simon Hughes, however, insisted that Mr Clegg's attack had been justified, and he warned that they could now ask the Electoral Commission to investigate the No campaign's "untruths".

With the opinion polls pointing to a No vote, some Tory MPs have expressed concerns that Mr Cameron will have to offer more concessions to Mr Clegg in order to bolster the position of the Lib Dems in coalition.

Mr Hague however insisted that would not happen.

"What we are doing in government is finding the right way forward together. It doesn't normally work in the manner of concessions to one side or the other," he said.

Mr Hughes said that the Lib Dems were right to be angry about the tactics used by the No campaign.

"The people responsible ought to back off, own up that they are inventing things to try to win the campaign for the status quo, and argue on the facts and merits of their case - which is a poor one - rather than try to frighten people to keep the present position," he told The Andrew Marr Show.

He singled out Tory Party chairman Baroness Warsi for "inventing facts" - such as claims that AV would help extremist parties like the far right British National Party (BNP).

He said that Mr Cameron had been "completely inaccurate" to claim that AV would require the purchase of expensive voting machines.

"If he has said that, then that is completely inaccurate. There are no voting machines. Everybody knows there will be no voting machines. I don't know whether that is deliberately lying or not but he is wrong about that," he said.

"I hope that even at this late stage people who have been peddling untruths will say that's not where we ought to go."

Mr Hague insisted that they had been raising legitimate issues for debate.

"There is no doubt that having a more complicated system costs more. That is a legitimate issue to raise in such a campaign," he said.

"The candidates in marginal seats are going to have to think about how they are going to get the second, third and fourth preferences of people who voted for the British National Party."

Mr Hughes said that if the No campaign was not prepared to correct these "untruths" before May 5, he would take up the issue with the Electoral Commission.

"I hope there might be public rebukes for those who said things that are untrue," he said.

Despite the bitter public recriminations, however, he insisted that the coalition partners would carry on working together, whatever the outcome of the referendum.

"The coalition will carry on for five years, I am clear about that. That is the deal that we did. We have to hold firm to that," he said.

He also acknowledged that the very public row would be welcomed by Lib Dem supporters who have complained that the party has been getting too close to the Conservatives.

"The really good thing about this campaign is that it has made sure that Liberal Democrats stand up for what we believe in and nobody will think we are Tories any more. Nobody can say in the future we and the Tories are the same," he said.